[pure-silver] Re: PMK was Re: Tri X film versions and sizes
- From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 17 Feb 2005 12:03:51 -0500
>What's your definition of superadditive and "superadditive ratio?"
AKAIK, the regular definition; that the activity of the two agents
combined is greater than the sum of their individual activities.
The optimum ratio can be determined by plotting the activity of various
mixtures. Data and graphs appear in Mason where he gives weight ratios
and molar ratios for Metol/hydroquinone and Phenidone/hydroquinone
combinations. An optimum ratio can be determined on the basis of
activity, film speed, or economy.
> In PMK the ratio is 1:20 which does not appear to be optimum.
Sorry 1:20 is a typo it should be 1:10 (5:50).
>Does that make it non-superadditive?
No, but the superadditive effect is overshadowed by the large amount of
pyro in comparison to the Metol.
As I stated, I have not seen any data as to the superadditivity of Metol
and pyro. The custom of adding a small amount of Metol to developers to
improve shadow detail goes back to the early part of the 20th century
(probably before the concept of superadditivity was recognized). I
believe this to be also the case with PMK rather than the intentional
creation of a superadditive developer. That was my point.
Jerry
-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Ryuji Suzuki
Sent: Wednesday, February 16, 2005 5:20 PM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: PMK was Re: Tri X film versions and sizes
From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
Subject: [pure-silver] Re: PMK was Re: Tri X film versions and sizes
Date: Wed, 16 Feb 2005 15:52:26 -0500
> Even so the superadditivity ratio of Metol to
> hydroquinone is around 1:3 or 1:4 and I would suspect that it would be
> in the same range for pyro.
What's your definition of superadditive and "superadditive ratio?"
> In PMK the ratio is 1:20 which does not appear to be optimum.
Does that make it non-superadditive?
> Metol has traditionally been added in small amounts to pyro developers
> to improve shadow detail and gradation. Any synergy between Metol and
> pyro in PMK is a lagniappe.
Does that make metol-pyrogallol non-superadditive?
--
Ryuji Suzuki
"Keep a good head and always carry a light camera."
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